The switch in the picture above is a Magura one. It is a microswitch rather than a pressure unit. I have a similar unit on my 88 Cali 3 and 88 Bonneville although they are not as long as the one shown.
Don, does that mean I can get one CHEAPER than £40, if so, where and what do I ask for. Wouldn’t happen to have parts numbers or anything would you… 
Shaun
The standard Magura one is usually about £6 plus postage, but they are shorter than the one Mike pictured above. They are like this
These are fitted to loads of european bikes. As i mentioned, these are a mechanical switch, not a pressure switch.
I do also believe there are a couple of thread options to look out for.
Don, I’ve found one for just under £6 which appears to be almost the same as the £40 one, so when it gets here we’ll see if it works…
Got to be worth a punt, I suspect that one day I’ll need it to pass an MOT, the nice man I take it too now, won’t be there forever. And he’ll be replaced by a spotty Oik that’ll only do things by the book… 
Thanks for your kind assistance in helping to keep me Beer fund at a constant level… 